820 MK. J. lUTCllIE ON UVDKOIDS [MuV 24. 



between the hydrothecae. Tliese are connected at the base of 

 each liydi'otheca by a strong bridge of caMiosarc, upon the middle 

 of which the base of the hyibunth rests. These structures 

 closely resemble those which Nutting has observed in Selaginopsis 

 ornaia (1904, p. 7), allowing for the differences in symmetry due 

 to the presence of four series of hydiothecfe in that species, in 

 place of two in this. Although each tube possesses a thick 

 definite ectoderm, I have been unable to distinguish the perisarc 

 which, Nutting supposes, surrounds each ccenosarcal tube. 



The structure of the polyp is like that of Thtiiaria rohusta. as 

 figured by Nutting (1904, p. 11, fig. 15). It has a large blind 

 sac, and clumps of large endodermal cells project into the 

 hydranth cavity except from the abcauline wall of the blind-sa<;, 

 w-here the development of the endoderm is insignificant. The 

 protractor band is attached, not to the abcauline wall of the 

 hydrotheca, but to varying points of the lateral wall in the 

 neighbourhood of the mai-gin of the hydi*otheca. 



The gonosome was not observed. 



Dimensions : — 



Stem, diameter 0*56-0'77 mm. 



Stem internode, length 2 mm. 



Hvdrotheca, length adnate 0*46-0'49 mm. 



free 0-07-0-14 mm. 



,, diameter at moutli 0'21-0'22 mm. 



Localities. St. 1, east of Tavoy Island and Port Owen, 4 to 12 

 fathoms, sand and bioken shells, and mud; several fragments. 

 St. 23, Five Islands, 8 to 12 fathoms, rock and sund. and mud; 

 one colony. St. 25, Gregoiy (iroup and Crichtoii Island, 4 to 14 

 fathoms, stones and broken shells, and I'ock ; one colony. 



Previously known only from Eastern and Northern Australia ; 

 Port Curtis and Holborn Island (Bale, 1884), Peel Island, 

 Moreton Hay (Pale, 1888), Flinders Passage. Toi-ivs Stiait 

 (Allman, 1888, as 77t.uiaria viiicta*), Thursdav Island (^^"eltner, 

 1900). 



Idia pristis Laniovu'oux, 1810, 



One of the commonest of the species in the collection, found at 

 eight of the foui-teen stations at which Hydioids were obtained. 

 There is much variability in the length of the free portion of the 

 hydrotheca, the sloping operculum appearing, in some cases, to 

 pioject directly from the suiface of the stem, while in others a 

 large jiart of the hydrotheca stands out at right angles to the 

 stem. Occasionally, too, the adcauline opercidum is lacking in 

 definiteness, the upjjer wall of the hydrotheca sim])ly meeting 

 the lower as an indefinite fia]». Many of the branches from 

 Station .'55 end in stolons, indistinguishahle iVom those which 

 ])i()ject fi'oni the hydrorhizal tubes. 



* See Uilluni, l'JU8, p. 2 of bcparuto fopy. 



